3 years ago

Cryptic Production of trans-3-Hydroxyproline in Echinocandin B Biosynthesis.

Wolfgang Hüttel, Johanna Mattay, Stefanie Houwaart
Echinocandins are antifungal nonribosomal hexapeptides produced by fungi. Two of the amino acids are hydroxy-l-prolines: trans-4-hydroxy-l-proline and, in most echinocandin structures, (trans-2,3)-3-hydroxy-(trans-2,4)-4-methyl-l-proline. In the case of echinocandin biosynthesis by Glarea lozoyensis, both amino acids are found in pneumocandin A0, while in pneumocandin B0 the latter residue is substituted by trans-3- hydroxy-l-proline (3-Hyp). We have recently reported that all three amino acids are generated by the 2-oxoglutarate-dependent proline hydroxylase GloF. In echinocandin B biosynthesis by Aspergillus species, 3-Hyp derivatives have not been reported. Here, we describe the heterologous production and kinetic characterization of HtyE, the 2-oxoglutarate dependent proline hydroxylase from the echinocandin B biosynthetic cluster in Aspergillus pachycristatus Surprisingly, l-proline hydroxylation with HtyE resulted in an even higher proportion (∼30%) of 3-Hyp than that with GloF. This suggests that the selectivity for methylated 3-Hyp in echinocandin B biosynthesis is solely due to a substrate specific adenylation domain of the nonribosomal peptide synthetase. Moreover, we observed that one product of HtyE catalysis, 3-hydroxy-4-methyl-l-proline, is slowly further oxidized at the methyl group, giving 3-hydroxy-4-hydroxymethyl-l-proline, upon prolonged incubation with HtyE. This dihydroxylated amino acid has been reported as a building block of cryptocandin, an echinocandin produced by Cryptosporiopsis sp.IMPORTANCE Secondary metabolites from bacteria and fungi are often produced by sets of biosynthetic enzymes encoded in distinct gene clusters. Usually, each enzyme catalyzes one biosynthetic step, but multiple reactions are also possible.Pneumocandin A0 and B0 are produced by the fungus Glarea lozoyensis They belong to the echinocandin family, a group of nonribosomal cyclic lipopeptides that exhibits a strong antifungal activity. Chemical derivatives are important drugs for the treatment of systemic fungal infections. We have recently shown that in the biosynthesis of pneumocandin A0 and B0, three hydroxyproline building blocks are provided by one proline hydroxylase. Here, we demonstrate that the orthologous proline hydroxylase from echinocandin B biosynthesis in Aspergillus pachycristatus produces the same hydroxyprolines, with an increased proportion of trans-3-hydroxyproline. However, echinocandin B biosynthesis does not require trans-3-hydroxyproline; its formation remains cryptic. While one can only speculate on the evolutionary background of this unexpected finding, proline hydroxylation in G. lozoyensis and A. pachycristatus provides an unusual insight into peptide antibiotic biosynthesis - namely the complex interplay between the selectivity of a hydroxylase and the substrate specificity of a nonribosomal peptide synthetase.

Publisher URL: http://doi.org/10.1128/AEM.02370-17

DOI: 10.1128/AEM.02370-17

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.